104 T. H. JOHNSTON. 



the thickness is only 0*04 mm., whilst the width gradually 

 increases from 0*2 mm. in the neck region to 0*35 mm. in 

 ripe segments. Thus the whole strobila is very thin and 

 narrow. To the naked eye, it appears like a piece of fine 

 white thread. Unless the intestine be carefully freed from 

 its contents by gently washing under water, the parasite 

 is likely to be overlooked. It adheres so firmly to the 

 tissues that it is not an easy matter to remove it without 

 injury. 



The scolex is somewhat pyriform, the broader end being 

 anterior. It lies buried in the mucosa which grows up 

 round it ; hence on removal of the worm, a pit-like depres- 

 sion remains. Its greatest width is from 0*32 to 0*4 mm., 

 this being in the region of the suckers. The length is 

 about 0*5 mm. The anterior end is prolonged into a short 

 thick, conical rostellum, about 0*14 mm. in diameter at the 

 base and 0*1 mm. in height. This structure is not retractile, 

 and instead of bearing hooks, it possesses an apical muscle 

 plug, an organ rarely met with in cestodes. In addition 

 to the rostellum, the scolex bears four typical suckers, two 

 dorsally and two ventrally. The cavity of each measures 

 0*08 mm. in diameter and 0*07 mm. in depth. The opening 

 is circular, the whole organ being subspherical. The layer 

 of muscle lining the cavity is about 16 micra thick, except 

 at the base of the hollow where it reaches 20 micra. The 

 musculature is thus comparatively powerful. The openings 

 are directed anteriorly and very slightly laterally (fig. 1). 

 The scolex becomes narrowed posteriorly to pass into the 

 long neck, the width of which is 0*16 mm. 



The strobila consists of very numerous proglottids that 

 are indistinguishable to the naked eye, excepting at the 

 end of the chain if mature segments be present, in which 

 case the segmentation is just visible. There is no trace of 

 overlapping of the anterior end of a segment by the 



